The present invention relates generally to systems and apparatus for improving the efficiency and operation of turbine engines, which, as used here and unless specifically stated otherwise, is meant to include all types of turbine or rotary engines, including steam turbine engines, combustion turbine engines, aircraft engines, power generation engines, and others. More specifically, but not by way of limitation, the present invention relates to systems and apparatus pertaining to seals for turbine engines and, specifically, to minimizing leakage flow between stationary and rotating parts of a turbine engine.
In many turbine engines, labyrinth seals are often used as a means of minimizing the leakage of working fluid between stationary and rotating parts. These stationary and rotating parts are generally radial in shape. In general, these seals include, on either the stationary or rotating part, multiple axially spaced teeth that are either machined integrally with, or inserted into the radial surface. Typically, the opposing radial surface is machined to provide axially spaced, protruding annular lands that, along with the radial surfaces between the lands, are regarded as part of the sealing assembly. The gap between the teeth and the high and low parts of the lands is called a “clearance” and maintaining minimal clearance is essential in minimizing the leakage of working fluid, which improves the efficiency of the engine.
However, operational transient conditions, which, for example, may include engine startup, shutdown, or load swings, often result in axial movement and radial expansion of the rotating parts in relation to stationary parts, which may cause the teeth or other structures that define the labyrinth seal on one radial surface to contact or collide with the teeth or structures on the opposing radial surface. This contact typically results in the wear of the teeth and the profiles of the radial surfaces. Such damage may result in a compromised seal and an increase in working fluid leakage.
Conventional steam turbine design practice generally requires a tradeoff between, on the one hand, providing effective sealing and, on the other, ensuring minimal damage to the seal. Existing seals may provide effective sealing, but their design results in subsequent damage to the seal due to axial movement of the rotor. Alternatively, other conventional seals prevent such damage, but require large clearances that do a poor job of sealing the flow of working fluid through the gap.